Transverse filters are multiple-stage spatial processing networks which allow for variable control of phase and/or amplitude response. Each stage, or tap, of a transverse filter includes a delay line and a leg. The delay lines of adjacent taps are coupled in series at a node. A signal applied to a tap is delayed a predetermined time interval by the delay line. The time interval is determined by the properties of the delay line material, i.e. the propagation constant, and by the geometry of the line layout, i.e. length and width. This is referred to as the "electric length" of the line. The delayed signal at each leg is applied to a multiplier. The attenuated signals of all taps are, in turn, summed at an adder. Phase/frequency equalizers are commonly applied to each delay line to avoid accumulation of phase/frequency and amplitude/frequency distortions of the delay lines at successive taps.
Variation in the electric length of taps in a filter, for example variation in the electric length of a delay line and/or the electric length of a leg can limit device performance. Assuming a trace delay of approximately 1.5 nsec per foot of trace, a difference in length between taps of as little as 1 inch can cause signals from different taps arriving at the adder to lag or lead each other by as much as 125 psec. In high-frequency applications, for example for the processing of signals of a frequency range on the order of 0.5 GHz, delay variations of such a high magnitude can have an adverse effect on filter response.
Variations in trace length of the leg between the node and the adder may be compensated for by selecting different delay line lengths for each tap. However, such a configuration would require different amounts of phase/frequency equalization at each tap and would complicate filter layout.